1. Field of Invention
This invention generally pertains to reactor cooling pump motors used in nuclear power facilities, and more particularly to a device for centering the motor shaft of a reactor cooling pump.
2. Description of the Prior Art
In nuclear reactor systems well known in the art, the nuclear reactor produces heat energy often in excess of 500xc2x0 F. which is transferred from the reactor core to steam generating equipment, such as heat exchangers, by a liquid phase reactor coolant that is circulated through the reactor core in a closed loop coolant system. Generally, the heat energy absorbed by the coolant is transferred by the heat exchanger to a second working fluid, resulting in a phase change of the second fluid from liquid to steam. Typically, to prevent the coolant in the closed loop from undergoing a similar phase change, the coolant is generally maintained at an extremely high pressure, well over 2000 psi, thus raising the phase change temperature of the coolant. In any event, the steam produced by the steam generating equipment is then used to generate electricity in a conventional manner.
As part of the above described process, a nuclear reactor coolant pump (RCP) is located in the cooling system and is used to circulate the reactor coolant between the reactor core and the steam generating equipment. Typically, each reactor will include four reactor coolant loops, with a separate reactor coolant pump and motor disposed in each loop.
RCPs are generally vertical type pumps with the motor mounted above the pump by means of a motor stand. The electric RCP motor has a vertical drive shaft that extends downwardly and is coupled with a vertical pump shaft extending up from the pump. As the RCP motor turns to drive the motor shaft, the motor shaft, being coupled to the pump shaft, drives the pump shaft which rotates the pump, thereby circulating the reactor coolant through the reactor system.
By way of example, a typical reactor coolant pump of the type described above includes an electric motor rated at about 8,000 Hp, 1,180 rpm, 13,500 V and having a high degree of cylindrical symmetry about the pump section. Such an RCP can pump over 100,000 gallons per minute through the coolant system. The vertical assembly stands approximately three stories high and is characterized by a pump bowl of approximately 6 feet in diameter and a motor of approximately 8 feet in diameter. The motor shaft itself is approximately 10 inches in diameter.
Commonly, the weight of the rotating elements of the RCP is carried by one of the motor bearings. The vertical shaft which connects the motor rotor to the pump is part of an assembly which includes the lower motor bearing and the pump seals. The pump seals are part of the primary system pressure boundary and must be maintained within the specified alignment parameters to minimize primary or reactor coolant system leakage. For this reason the motor drive shaft must be maintained in a xe2x80x9ccenteredxe2x80x9d position during operation. Shaft alignment for the pump seals and the motor drive shaft is maintained by the motor bearings. Any excessive play in the lower motor bearing, namely the radial bearing around the shaft at the lower end of the vertical motor, would jeopardize not only the motor, but also the pump and pump seal. If the pump seal fails, reactor coolant can leak from the primary system.
In any event, after a period of operation, it is generally necessary to perform routine maintenance on certain RCP motor components, including the motor shaft, pump seal and bearings, to ensure stringent alignment of all components at all times. During maintenance, each lower motor bearing is tested for wear which could result in radial movement of the motor shaft. If a bearing is worn excessively, it is replaced in order to limit such radial movement, thereby avoiding damage to the pump seal, pump and motor.
The process used to establish and maintain proper bearing and coupling alignment involves the use of shaft pushers to apply radial pressure to the motor shaft. Generally, four shaft pushers are temporarily mounted beneath the lower bearing oil pan at four positions around the shaft, 90 degrees apart. Each pusher can then be adjusted as needed to move or maintain shaft position as dictated by two specific maintenance functions.
First, pushers are used to test wear on the lower motor bearing. This bearing wear test or xe2x80x9cswing checkxe2x80x9d is accomplished by applying radial pressure to the shaft at each compass point, thus pushing the shaft horizontally to its extreme so that deviation from the shaft centerline can be measured and used to determine bearing wear. Second, pushers are used to ensure axial alignment of the shaft during shaft coupling assembly. Only a well-aligned coupling will enable the motor and the pump to run for a full fuel cycle without excessive wear.
All of the above-described maintenance occurs when the pump is not in operation. However, maintenance on the RCP motor is often difficult because the area under the motor stand is approximately four feet in diameter and three feet in height. In addition to the limitations imposed by this physically small space, maintenance personnel must also be aware of other hazards that could inhibit or hamper maintenance to the motor, such as a relatively high radiation environment, rotating machinery and thermally hot metal parts.
Installation of the temporary pushers of the prior art required removal of a series of bolts along the joint flanges of the lower bearing oil pan. Bolt removal included removal of the lockwire used to secure the bolts. The lockwire was typically treated as radioactive waste and had to be properly disposed. Further, removal of these bolts often resulted in leakage of the radioactive oil contained in the pan. Since the maintenance personnel could only access this area from below, any leaking oil was likely to fall directly onto the personnel as they installed the temporary pushers. The flange bolts were then used to mount the temporary pushers to the oil pan flanges for the various maintenance activities. After use, the pushers were removed and the bolts were reinstalled, torqued and lockwired. Typically, installation and removal of prior art pusher tools required several hours of work by one to two maintenance personnel. More significantly, the procedure resulted in radioactive waste and exposed the maintenance personnel to the various hazards discussed above.
The present invention provides a pusher tool that utilizes a clamp assembly that fits over the existing bolts and nuts of the oil pan flanges without disassembly of the RCP motor. The clamp assembly supports a pusher that can be used in the standard fashion for maintenance activities.
The pusher tool is formed of two plates, each plate having holes disposed to fit externally over the bolt heads of the oil pan flanges. One of the plates has a spacer block through which a threaded positioning shaft is inserted. The threaded positioning shaft has a motor shaft pusher block mounted to its distal end. The two plates, when mounted over the bolts of the oil pan flanges, are attached to one another by fasteners that can be adjusted in position with wing nuts. This allows tightening of the plates together over the bolt flanges thereby clamping the tool to the flanges of the oil pan. The pusher block can then be adjusted into place against the motor shaft by means of the threaded positioning bolt.
The present invention, by forming a pusher block support clamp that fits over the bolts and flanges of the oil pan, overcomes the need for removing the bolts securing the oil pan flanges together. By avoiding such oil pan bolt removal, the pusher can be installed quickly and easily without the need for prolonged exposure by maintenance personnel to the hazardous environment of a nuclear reactor cooling pump.